Looking for advice/experience re: next steps after a cancer diagnosis and possible spread to the lungs

Hi guys, going to try to keep a long story short.

My vet found a mass on my 15yr old cat’s paw two weeks ago and did a cytology. It came back malignant last Monday – they think soft-tissue sarcoma but haven’t ruled out lung-digit syndrome.

We then did a chest xray to see if there was any spread. The chest xray does show a small pulmonary nodule (like less than 1.5cm) that I’ve been told COULD be unrelated to the cancer, but could obviously also be related to metastasis.

The next step is an oncology appointment. Based on research, I’m assuming my options are going to be:

1. Lung biopsy to see if the pulmonary nodule is malignant
2. Amputation of his leg and biopsy of the mass on his paw
3. Continued monitoring of the nodule to see if there’s any growth
4. Palliative care

Once I have the options/costs laid out for me I’ll be able to move forward. What I don’t want to do is spend thousands of dollars on a biopsy or a surgery just to lose him in a couple of months. He’s an old kitty, and I’m leaning toward palliative care. But I also know I’d feel so guilty if the cancer hadn’t actually spread and it turns out he would’ve been a good candidate for amputation/surgery.

I wish they could just tell me something like “there’s a 70% chance the cancer has spread to his lungs and the nodule is malignant” or “because the x ray of his paw doesn’t show any bone involvement and his lymph nodes aren’t swollen, there’s a good chance it’s benign.”

But I know that isn’t realistic and there are likely going to be some expensive tests. I guess I’m just looking for similar experiences/words of wisdom before I go to the oncologist? How can I keep this as cost-effective as possible without being wracked with guilt for not exploring every possible option or doing every possible test?